Stock market just had worst 10 years in history

Out of curiosity, I took the S&P 500 annual return data since 1926, calculated the index’s moving 10-year returns and produced the chart below. Two things are worth noting:

1. The 10 years ending 2008 are the worst ever for the index, with a total return of -13%.

2. The S&P 500’s 10-year return dynamic seems to follow a periodic pattern. The second worst 10-year period ended in 1938 (-9%); and the third worst 10-year period ended in 1974 (13%）, almost right in the middle of 1938 and 2008. Serendipity?

The market is in a trough. A chart can not predict the future, but if it can, things can only get better from here.